Metal organic frameworks offer a degree of predictability in the topology of the resulting structures. The primary MOF geometry (i.e., the shape of the secondary building unit (SBU) from which the MOF is constructed) can be influenced by both the linker shape and the metal coordination geometry. The ultimate structure observed in the solid-state can therefore be predicted in ideal cases by considering typical metal ion and/or ligand coordination preferences. This can lead to the generation of homologous series, such as O. Yaghi’s isoreticular IRMOF materials), and can allow materials properties that are influenced by the solid state structure to be tuned in a rational manner. We report here two distinct Zn-stilbene MOF structures that exhibit different solid-state emission profiles, resulting from important differences in stilbene-stilbene distances in the two different geometries. We found that variation in the reaction conditions between stilbene dicarboxylic acid and zinc nitrate affords both 2D and 3D geometries, with the difference between materials (and, hence, in structure) clearly evident upon observing the luminescence color. This is a result of competition between two possible coordination geometries and the ability of DMF to behave as a ligand. In addition, we report changing the metal ion to give a series of isostructural 2D structures with the generic formula M3L3(DMF)2 by utilizing similar growth conditions. Here, the observed luminescence is solely a function of the stilbene-stilbene geometry, not the metal. The emission spectra are similar, only varying in intensity due to the presence of a quenching paramagnetic metal (Mn). Finally, we report on a novel phenomenon whereby we are able to modulate the secondary structure of a MOF (i.e., generate structures with the same SBU geometries but with different arrangements of these SBUs with respect to each other) through subtle variations of the ligand electronic structure by incorporating the linker azobenzene dicarboxylic acid. Theoretical and experimental results will be presented.

Effect of intermolecular forces and linker on metal organic framework secondary structure

251st National Meeting (2016)

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